Popular social media reports are then often picked up by traditional media outlets.

While some of these stories are flat out fabricated, a sizable chunk are old stories masquerading as new. The new fakes require reporting before they can be dismissed outright, but the recycled stories should be relatively easy to stamp out quickly.

Some stories out of Nice have been both old and phony, like the outrageous accusation that a Canadian Sikh man was behind the attack (making the rounds again after fooling several media outlets following the Paris attacks in November) or this plea for help finding a missing relative.

In late June, it was established media outlets as well as social media users who confused old for new. One of the most blatant examples of this was leading Italian daily La Repubblica describing the attacks on the Turkish city on its homepage with photos from the terrorist attack on the Brussels airport months before.

The Brexit referendum has also led to old stories resurfacing as new. This tweet about The Sun publishing a tiny correction on a tremendously misleading story about the EU was posted last Tuesday and racked up more than 8,000 retweets — despite being almost three years old.

Similarly a 2015 article with a quote by Queen Elizabeth on Europe being "its continent," where the "it" was Britain, made the roundsonsocialmedia again after the referendum results were announced a year later.

Perhaps most famously, after the Paris attacks millions of people shared a six-month old story of a massacre at the Kenyan university in Garissa (and hundreds of thousands did so again after the Orlando shootings).

In all these cases, either the simplest of online searches or looking at the timestamp of the article would have sufficed to avoid resurrecting the old story as a new one. But is there anything media outlets and social networks could do to prevent this?

"I think it's really hard to find a way for social networks to automatically flag the origin of an image," Silverman said.

Social networks "probably could" do more, "but news organizations and journalists can do it right now," said Alastair Reid, managing editor of First Draft News. "The Guardian has a 'this article is X months old' text to the left of old stories. Whether people read it is another matter."

Media outlets have a big role to play, Silverman said, especially with recurrent fakes whose debunks can be published as soon as they start resurfacing. "It seems like the best defense against this is for news outlets and other influential people to actively communicate that these claims are false when they begin to kick up after an event. If we know it will happen let's be ready to knock it down quickly."

The format of a debunk is also crucial, Reid said, referencing an analysis from Chris Blow of Meedan, a First Draft News partner. "Saying 'this picture is from 2013' in a tweet with the picture is a good start," Reid said. "But it still shares the picture and that can be taken and shared again, without the text saying it's old."

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Alexios Mantzarlis joined Poynter to lead the International Fact-Checking Network in September of 2015. In this capacity he writes about and advocates for fact-checking. He also trains and convenes fact-checkers around the world.